Sen. Ted Cruz accused President Obama of underestimating and misjudging the threat posed by ISIS, but said he should seek congressional approval before deciding whether to escalate the military campaign against the Islamic extremists.

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“What we ought to have is a directed, concerted, overwhelming campaign to take them out,” Cruz said in an interview on “This Week.” “The focus should be Iraq, but the real focus should be taking out ISIS. Within Syria, it should not be our objective to try and resolve the civil war.”

Cruz, a Texas Republican, said the president “has not demonstrated that he’s taking ISIS seriously.” Even as Cruz delivered a blistering critique of the administration’s foreign policy, he conceded that Republicans have their own foreign policy debate unfolding inside their party, which he said makes him more inclined to seek the presidency.

“The American people in 2014 and also November 2016 are going to be looking for leaders who want to work to restore America’s leadership in the world,” Cruz said.

When pressed whether the challenges abroad made him more inclined to open his own bid for the Republican presidential nomination, he declared: “It increases my interest in doing everything I can to change the direction we’re on.”

Not all Republicans agree with Cruz’s view that the president should seek congressional approval. Sen. Marco Rubio, R-Fla., sent a letter to the White House on Friday, saying the president should act swiftly without the input of Congress.

For Republicans eyeing the White House in 2016, early divisions are becoming clear.

Sen. Rand Paul now says he would "destroy ISIS militarily." But his tough talk is at odds with his earlier views, which prompted him to write an essay this week in TIME Magazine, titled: "I am Not an Isolationist."

When asked whether he agreed, Cruz demurred, but did not come to Paul’s defense.

“Oh look, I’m going to let Rand characterize his own views,” Cruz said. “And I will leave that to the American people to make their own judgments.”

Among some grassroots Republicans, there is a growing non-interventionist strain with deep resistance to another war.

Louisiana Gov. Bobby Jindal, also visiting New Hampshire over the weekend, said it was a fine and dangerous line for the party to walk.

“The country, the world, needs America to be strong and predictable,” Jindal told “This Week.” “The world is getting more dangerous and less predictable because of a lack of American leadership.”

ISIS, along with a growing list of foreign policy challenges, are already front-and-center in the early stages of the 2016 campaign. Positions staked out now are likely to become a lasting part of a candidate’s record.

“It is absolutely true that there is a war weariness. We are tired of sending our sons and daughters to find in distant battles for years,” Cruz said, but added: “I don’t think the American people are at all reluctant to defend America. They’re just not interesting in nation building.”